The objective of this research is to elucidate the molecular mechanisms that mediate and that regulate transcription of Xenopus rRNA genes. A major goal of the proposed experiments is to identify and determine the role of the nucleotide sequences and (protein?) factors that specify rRNA initiation. Apparantly multiple factors are involved, for a much larger rDNA region is required for initiation in vitro (about 150 bp) than in microinjected oocytes (about 20 bp). The functional rDNA regions will be identified and characterized by analysis of in vitro constructed rDNA mutants, using the oocyte microinjection and the in vitro transcription systems that we have developed. We will determine the initiation specificity afforded solely by RNA polymerase I and will attempt to identify the additional requisite factors by fractionation and reconstitution studies. A second goal of this proposal is to develop an understanding of the process of rRNA termination by similar procedures. A third major goal of this research is to learn about the factors that regulate rRNA transcription. Initially these studies will focus on analyzing the mechanism of an exciting preliminary result - that the Cytomegalovirus genome specifically represses rRNA initiation - but other instances of rRNA regulation will also be persued. The final goal of this project is to learn about RNA processing, determining the mechanism of rRNA cleavage as well as the polymerase specificity of various RNA processing events. Not only will this research significantly add to our basic knowledge of transcription of rRNA, a crucial and prevelent RNA species, but we hope our results will also allow disease related effects of rRNA transcription to be better understood.